1. Field of the Invention
The present invention relates to a vehicle lamp and a method of manufacturing the vehicle lamp. More specifically, the present invention relates to a technique of reliably joining a housing, inside of which a light source, etc. is housed, and a transparent cover, which closes a front opening of the housing.
2. Background Art
In a method of manufacturing a vehicle lamp such as a lamp for an automobile, it is necessary to attach a transparent cover, generally called as a lens, to a housing so as to cover a front opening thereof.
When attaching the transparent cover and the housing, the related art generally employs a method in which a seal leg is protrusively provided at a peripheral edge portion of the transparent cover while a groove for receiving the seal leg is formed on the housing. The seal leg of the transparent cover is received by the groove of the housing via a sealing material or an adhesive. According to this attaching method, the seal leg and the groove are provided so as to protrude outwardly from the peripheral edge portions of the transparent cover and the housing. Thus, when seeing the transparent cover from a front side, there appears a portion having a relatively large area where light does not pass through (that is, a dark portion) at the peripheral edge portion of the transparent cover. Therefore, there has been a problem that a light irradiation area is relatively small as compared with the entire size.
In view of such a problem, there has been proposed a method in which the seal leg of the transparent cover is directly joined to a joining surface portion of the housing. When the seal leg of the transparent cover is directly joined to the housing, a width of a joining space is quite small and, thus, the dark portion at the peripheral edge portion of the transparent cover can be made smaller. As a means for such a direct joining, there have been generally employed hot plate welding, vibration welding, etc. According to these means, the joining is performed in such a manner that, at the joining portion between the transparent cover and the housing, materials of the transparent cover and the housing exist in a mixed molten state, and then are cooled and solidified. However, there is a problem that excessive molten materials stick out from the joining portion, thereby deteriorating an appearance when the stuck out portion is seen from the front side via the transparent cover.
Further, because configurations to which the above methods can be applied is limited (e.g., an inclination angle is limited; it is required to be substantially flat in a vibration direction in the vibration welding, and it cannot be steeply inclined with respect to a pressing direction of a hot plate in the hot plate welding), these methods cannot cope with the recent needs of a three-dimensional design.
There has been proposed another method in which the transparent cover is joined to the housing by laser welding. According to the laser welding, a molten state of the materials (that is, irradiation energy at the joining portion) can be controlled to be constant by controlling a laser output, a spot diameter at the joining portion, and a scanning speed. Thus, the sticking-out of the molten materials due to the excessive melting can be prevented, thereby enabling the method to cope with a complicated configuration. When a laser light is transmitted through the transparent cover and irradiated on the housing, the housing is heated and molten, and the heat is transmitted to the transparent cover, whereby both the transparent cover and the housing are molten and are adhered to each other.
However, according to a light welding, such as the laser welding, a defective joining occurs when a welding portion of the transparent cover and a welding portion of the housing are not reliably in contact with each other.
Nevertheless, because the transparent cover and the housing of a vehicle lamp are resin molded parts, it is difficult to obtain a shape in conformity with the actual design due to an influence of a warpage or a flexure after the molding. Thus, it is difficult to surely make the transparent cover contact with the housing along the entire periphery thereof. When the transparent cover is not surely made in contact with the housing, the heat applied to the housing by the irradiation of a light ray, such as laser light, cannot be transmitted the transparent cover and, thus, the welding cannot be performed.